It is well known that in vacuum furnaces the hot zone chambers are usually constructed with a generally cylindrical outer wall, some form of heat shield (to contain the heat within the hot zone chamber) secured to the inside of the outer wall and a heating element formed to generally follow the contour of the inside surface of the outer wall but formed to fit within the hot zone chamber. Such heating elements are subject to expansions and contractions as a result respectively of the heat generated by electrical energy passing therethrough and alternatively as a result of the cooling, experienced when the electrical energy is terminated. Such expansions and contractions cause stresses in the heating element material and eventually resultant fractures occur therein. As a result of such damage it has been the practice to replace the heating element, or at least sections thereof. Hence the need for a mounting means which will enable the heating element to be easily mounted or removed becomes apparent. Despite the apparency of the need for means to permit an easy mounting or easy removing of a heating element or a section thereof, such mounting means has not been provided in the prior art. It is my belief that my present invention fulfills that need.
In addition other infirmities have been inherent in prior art heating element arrangements for vacuum furnaces. The heating elements generally have had apertures therein to accommodate some form of holding means passing therethrough. Such apertures reduce the material through which electrical current may flow hence increasing the current density at such locations and thereby literally burning out such areas. I have provided a means to compensate for the material removed to form the aperture in the heating element, hence negating an increase in current density and removing a major cause for heating element failures.
Another infirmity (to which I made reference above), with respect to the heating element arrangement lies in the fact that the heating element very often gets electrically "shorted out" to the mounting structure by deposits of electrically conducting material (which vaporizes from materials being heated in the furnace), providing the "shorting" paths. The vaporized material "builds up" to provide an electrical path between the heating element and the mounting means which in turn provides an electrical path to ground. Such short circuits result in arcing and destruction of part of the heating element. My present invention dramatically reduces the possibility of short circuits resulting from material build ups caused by vaporized material from work pieces within the heating chamber.